This invention relates to a hydraulic control system for off-highway self-propelled work machines, such as construction and industrial vehicles, of the type having at least one variable displacement pump to be placed in and out of communication with one or more such driven components as a propelling motor and implement actuators. More specifically the invention concerns such a system for automatically controlling the per-cycle displacement of the pump in accordance with whether the pump is in or out of communication with the driven component or components.
A variable-displacement hydraulic pump or pumps are usually incorporated in such off-highway work vehicles as an excavator, which uses hydraulic power for propelling the vehicle, for swivelling the upper frame relative to the undercarriage, and for actuating the implement assembly. The hydraulic system of such work vehicles usually includes a servomechanism, acting on the swash plate of the pump, for maximizing its per-cycle displacement when the load is small. This possesses the disadvantage that the pump displacement is at a maximum even when the pump is out of communication with all the driven components, thus causing considerable waste of energy.